1. Field of the Invention
The present disclosure relates to flat panel displays, and more particularly, to liquid crystal displays (LCDS) and methods of fabricating LCDs.
2. Description of the Conventional Art
A flat panel display (FDP) generally has a slim profile and provides a flat picture. One type of flat panel display is a liquid crystal display (LCD), which is widely used as a monitor of a notebook computer and the like. The LCD includes two substrates attached to each other, and a liquid crystal layer interposed between the two substrates. By applying different voltages to the two substrates, respectively, an electric field is formed. When the electric field is applied to the liquid crystal layer, liquid crystal molecules of the liquid crystal layer are re-aligned to vary a light transmittance of the liquid crystal layer, so that a desired image is displayed.
On a lower substrate of the two substrates, a plurality of pixels is regularly arranged. Each of the pixels includes a main pixel and a sub pixel. The sub pixel is to express colors. The sub pixels corresponding to a number of basic colors constitute a single main pixel. For example, when red (R), green (G) and blue (B) colors corresponding to three primary lights are used, a single main pixel includes three sub-pixels corresponding to the respective colors. Alternatively, the single main pixel includes four sub-pixels further including a white sub-pixel so as to increase a transmittance efficiency. The above three color sub-pixels structure and the four color sub-pixels structure have a difference in operation as follows.
A plurality of gate lines and a plurality of data lines intersecting the plurality of gate lines are formed on the lower substrate of an LCD. Regions defined by the plurality of gate lines and the plurality of data lines intersecting each other correspond to the sub-pixels, each having a pixel electrode formed thereon. Data signals are applied to the data lines and transmitted to pixel electrodes, so that an electric field is applied to the liquid crystal molecules of the liquid crystal layer arranged on the pixel electrodes. Then, when the electric field is applied only in the same direction, the liquid crystal molecules are always inclined only in one direction due to a property of the liquid crystal, thereby deteriorating the liquid crystal molecules. To avoid such deterioration of the liquid crystal molecules, a positive (+) voltage and a negative voltage (−) are alternately applied to the pixel electrode. For the positive sub-pixels and the negative sub-pixels to be uniformly distributed, a data voltage with a different polarity is applied between sub-pixels adjacent to each other in a gate direction.
In the case of the three color sub-pixels structure, the sub-pixels arranged in the gate line direction are applied a data voltage with polarities, such as “red (+)/green (−)/blue(+)/red(−)/green(+)/blue(−) . . . ”. In the case of the four color sub-pixels structure, the sub-pixels arranged in the gate line direction are applied a data voltage with polarities, such as “red (+)/green (−)/blue(+)/white(−)/red(+)/green(−)/blue(+)/white(−) . . . ”.
In a case of the three color sub-pixels structure, the red sub-pixels are arranged with alternating positive polarity and negative polarity, whereas in a case of the four color sub-pixels structure, the red sub-pixels are arranged all only with the positive polarity. In other words, in the three color sub-pixels structure, since a number of the sub-pixels constituting the main pixel is an odd but the types of the polarity are two, their polarity correspondence is changed. In other words, the red sub-pixels have both the positive polarity and the negative polarity. In the four color sub-pixels structure, since the number of the sub-pixels constituting the main pixel is an even and the types of the polarity are two, their correspondence is not changed. In other words, the red sub-pixels have only one polarity in a specific frame.
When the sub-pixels of a specific color have only one polarity, an image display quality is lowered. In other words, while the polarity of the pixel electrode is periodically inverted from the positive polarity to the negative polarity or vice versa, the light transmittance of the liquid crystal layer is varied against the two polarities. For instance, in a case where only the red color is displayed, when a positive voltage is applied to all the red sub-pixels in a present frame and a negative voltage is applied to all the red sub-pixels in a next frame, a flicker occurs due to a transmittance difference between the opposite polarities during an inversion operation. Further, when only the positive voltage is applied to the sub-pixels, a voltage applied to the upper substrate is distorted. Thus, the electric field applied to the liquid crystal is greater or less than that in an ideal circumstance, thereby deteriorating the image display quality.